Answer: Eating breakfast.
This is interesting. Researchers tested a group of healthy volunteers (college students) and looked at the effects of several treatments on the concentrations of sulfur-containing gases, compounds thought to be responsible for morning breath. Upon awakening in the morning they collected oral gas samples immediately and then for the 8 hours following. Treatments included no treatment, brushing the teeth with toothpaste, breakfast ingestion, and three other interventions. They found that “Brushing the teeth had no apparent influence on the sulfur gases.” and “Ingestion of breakfast resulted in strong trends toward decreased sulfur gases.” As an aside, another treatment was swallowing of capsules for bad breath relief. It had no effect.
So what is the takeaway? I think that because there is such a large concentration of bacteria that cause bad breath on the back of the tongue (tongue scraping did help a little in this study) and the throat area, that many of these bacteria were loosened up and swept away with the eating process. This likely was the cause of lower amounts of sulfur gases being produced. Since the bacteria weren’t located where the toothbrush and paste were applied, it provided no improvement.
Bottom line: The back of the tongue and throat area seems to be associated with breath odor issues. This explains why our method of gargling is so effective.